Yep, I tip 20% for Gardengrocer. I have used them twice and was very happy both times. I got everything that I ordered, delivered on time. It's a great service!
I agree with the 20%...we have used them four times and I believe the bigger tip helps. Each time the delivery person has called me when I was still at the airport to say he was at the resort. I tell him to check the items with bell services and our stuff is brought up to the room with the rest of our items from the Magical Express.